Up to now, it is well known that Long Term Evolution (LTE) systems are deployed to operate in licensed carriers. However, with the evolution of the LTE, some companies (such as Qualcomm) in the second half of 2013 proposed and suggested to study on the subject of the deployment of the LTE in unlicensed carriers. However, it has not yet been accepted by the LTE and a project thereof has not yet been set up by the LTE.
Qualcomm gives the reasons for the project, which are primarily that with the rapid growth of data services, in the near future, the licensed spectrum can no longer bear such a huge amount of data. It is recommended to consider deploying the LTE in an unlicensed spectrum to share the data traffic in the licensed carrier through the unlicensed spectrum.
The unlicensed spectrum has the following characteristics:
1. It is free of charge/has a low cost, there is no need to buy the unlicensed spectrum for use, and a cost for the spectrum resources is almost zero;
2. The access requirements are low, the cost is low, individuals and companies can participate in the deployment, and devices of any equipment manufacturer can be used.
3. Resources can be shared, and when a number of different communication systems are operating in the unlicensed spectrum, or different operators of the same communication system are operating in the unlicensed spectrum, some manners for sharing resources can be used, which improves the spectral efficiency.
4. There are a lot of wireless access technologies, which can be across different communication standards and are difficult to collaborate, and the network topologies are diverse.
5. There are a lot of wireless access sites and a number of users, which are difficult to collaborate, and results in a large centralized management overhead.
6. There are a lot of applications, in which a variety of services can operate, such as Machine to Machine (M2M) communication, and Vehicle to Vehicle (V2V) communication.
The above-mentioned basic characteristics determine that the unlicensed spectrum may be an important evolution direction of the wireless communication system, but there are also many problems at the same time. For example, there will be a variety of wireless systems in the unlicensed spectrum which are difficult to coordinate with each other and which interfere with each other.
The LTE is deployed in the unlicensed carrier, and there is still a need to support the regulations for the unlicensed carrier. Most countries require communication systems to support the listening first then speaking mechanism when the communication systems are deployed in the unlicensed carrier. Through the listening first then speaking mechanism, it can avoid interference of adjacent systems to each other due to the use of unlicensed carriers by the adjacent systems at the same time. In addition, a contention mechanism is further introduced, that is, adjacent system sites (usually adjacent sites of the same system) can avoid the interference due to the use of the unlicensed carriers by the adjacent sites of the same system at the same time through the contention mechanism.
For a LTE system, during contention in a designed contention window, an LTE base station may contend for unlicensed carrier resources at any time, that is, a time when the LTE base station contends for a right to use the unlicensed carrier is mostly not aligned with the beginning of a subframe of the LTE system. The base station often acquires the right to use the unlicensed carrier at a time within a subframe. However, according to the scheduling mechanism of the LTE system, a scheduling time is in units of subframes, and then how to use resources in a period of time from the time when the base station contends for the unlicensed carrier up to a start time of a next subframe is a problem to be solved.